Integrated circuit switches used in integrated circuits can be formed from solid-state structures (e.g., transistors) or passive wires (MEMS). MEMS switches are typically employed because of their almost ideal isolation, which is a critical requirement for wireless radio applications where they are used for mode switching of power amplifiers (PAs) and their low insertion loss (i.e., resistance) at frequencies of around 1 GHz and higher. MEMS switches can be used in a variety of applications, primarily analog and mixed signal applications. One such example is cellular telephone chips containing a power amplifier (PA) and circuitry tuned for each broadcast mode. Integrated switches on the chip would connect the PA to the appropriate circuitry so that optimized performance for each mode can be obtained.
Depending on the particular application and engineering criteria, MEMS structures can come in many different forms. For example, MEMS can be realized in the form of a cantilever beam structure. In the cantilever structure, a cantilever arm (suspended electrode with one end fixed) is pulled toward a fixed electrode by application of an actuation voltage. The voltage required to pull the suspended electrode to the fixed electrode by electrostatic force is called pull-in voltage, which is dependent on several parameters including the length of the suspended electrode, spacing or gap between the suspended and fixed electrodes, and spring constant of the suspended electrode, which is a function of the materials and their thickness. Alternatively, the MEMS beam could be a bridge structure, where both ends are fixed.
MEMS can be manufactured in a number of ways using a number of different tools. In general, though, the methodologies and tools are used to form small structures with dimensions in the micrometer scale with switch dimensions of approximately 5 microns thick, 100 microns wide, and 200 microns long. In addition, many of the methodologies, i.e., technologies, employed to manufacture MEMS have been adopted from integrated circuit (IC) technology. For example, almost all MEMS are built on wafers and are realized in thin films of materials patterned by photolithographic processes on the top of the wafer. In particular, the fabrication of MEMS uses three basic building blocks: (i) deposition of thin films of material on a substrate, (ii) applying a patterned mask on top of the films by photolithographic imaging, and (iii) etching the films selectively to the mask.
However, the typical manufacture of MEMS also includes the transmission line and the MEMS switches being built separate, which can lead to decreased isolation and increased parasitic insertion loss. Although commonly used millimeter wave switches, such as switches comprised of SiGe HBT or GaAs pHEMT, have insertion loss typically of ˜0.1 to 0.3 dB over 30-110 GHz and isolation typically of ˜20-30 dB over 30-110 GHZ, the millimeter wave switches consume power for operation of the integrated circuit. The silicon on insulator (SOI) and complementary metal-oxide-semiconductor (CMOS) field-effect-transistors (FET) typically have high insertion loss and poor isolation at high frequencies. Moreover, metal ohmic contact MEMS switches are expensive and have not been produced on a large scale due to resistance degradation during cycling lifetime.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.